Position control methods for an axle are generally known. Generally an instantaneous actual position value and an instantaneous setpoint position value are predefined for the position controller. The position controller determines an instantaneous manipulated variable according to a predetermined controller characteristic and actuates the axle according to the instantaneous manipulated variable. The controller characteristic can for example be a P, PI or PID controller characteristic. Further control circuits (for example a speed controller and/or a current regulator) can in some instances be subordinate to the position controller.
The procedure in the prior art produces satisfactory results in a plurality of applications. For some applications, where a high level of accuracy and rapid correction of control differences (i.e. the difference between the actual value and the setpoint value) are required, additional measures are however necessary.
It is thus known for example in the prior art that a speed controller can be subordinated to the position controller, to determine a speed pre-control value based on the temporal derivation of the setpoint position value (in other words the difference in relation to the temporally preceding setpoint position value, divided by the position controller cycle) and to apply the speed pre-control value additively to the manipulated variable of the position controller. This approach results in a smaller control deviation only in the case of essentially regular changes to the setpoint position value. It is also necessary to filter the instantaneous setpoint value supplied to the position controller. Otherwise there is a risk of controller instability.
In the prior art it is also known that a current regulator can be subordinated to the speed controller in addition to the speed pre-controller, to determine a current pre-control value for the current regulator based on the second temporal derivation of the setpoint position value and to apply the current pre-control value additively to the manipulated variable of the speed controller. This approach results in small control differences even in the case of irregularly changing setpoint position values. However the controller responds to manipulated variables in a very sensitive manner and tends toward instability.
In the field of large industrial units (for example for continuous casting plants and rolling mills) it is known that a so-called generalized predictive control (GPC) can be implemented. With such a type of control a number of future setpoint values are supplied to the controller in addition to the instantaneous actual value and the instantaneous setpoint value. The controller uses a model of the unit to be controlled to determine an instantaneous manipulated variable and actuates the unit to be controlled according to the instantaneous manipulated variable. The manipulated variable is determined in such a manner that an overall deviation of the instantaneous and future actual values from the corresponding setpoint values is optimized according to a predetermined evaluation function. For the last-mentioned type of control, see also for example the technical article “Generalized Predictive Control (GPC)—Ready for Use in Drive Applications?” by R. Kennel et al., University of Wuppertal and GB 2 402 499 A.
A similar disclosure content to that of the technical article by R. Kennel mentioned above is known from the technical article “Real-Time Application of Neural Model Predictive Control for an Induction Servo Drive” by D. Neumerkel et al., Control Applications, 1994/IEEE, vol. 1, Aug. 24, 1994, pages 433 to 438.
A position control method for an axle is known from FR 2 689 260 A, having the following features:    An instantaneous actual position value, an instantaneous setpoint position value and a number of future setpoint position values and for each future setpoint position value a value characteristic of its temporal offset in relation to the respectively immediately preceding setpoint position value are predefined for a position controller.    The position controller uses a model of the axle to determine an instantaneous manipulated variable and for the future setpoint position values an expected manipulated variable and an expected actual position value respectively.    The position controller determines the instantaneous manipulated variable, the expected manipulated variables and the expected actual position values in such a manner that an overall deviation of the instantaneous actual position value and the expected actual position values from the corresponding setpoint position values is optimized according to a predetermined evaluation function.    The position controller actuates the axle according to the instantaneous manipulated variable.
With the position control method known from FR 2 689 260 A it is possible to control the position of the axle with a good level of control accuracy while at the same time achieving a high level of control dynamics and yet low susceptibility to interference.
With the position control method known from FR 2 689 260 A the setpoint position values per se are supplied to the corresponding control facility.